Epoxy compositions have long been known as compositions possessing an excellent balance of properties such as good adhesion, i.e. shear strength, low shrinkage upon cure, dimensional stability, hardness, and corrosion and solvent resistance. See Pottick, L. A., "Kraton.RTM. Rubber Modified Epoxy Blends," 34th Int. SAMPE Sym. May 8-11, pp. 2243-2254 (1989). However, when cured, epoxy alone tends to be brittle and exhibits low or no peel strength at room temperature and especially at colder temperatures. As a result, there have been attempts to modify epoxy compositions in order to counteract the epoxy's brittleness, thereby enhancing the peel strength of the compositions. Such strengthened compositions are especially desirable in applications in which the compositions will be exposed to a wide range of temperatures.
Past attempts to modify epoxies involved reacting them with copolymers of butadiene, acrylonitrile or other "rubber"-based compositions. See Pottick, supra; and Journal of Applied Polymer Science, Vol. 26, pp. 907-919 (1981). By reacting an epoxy with those compounds and then processing the modified composition to induce in situ phase separation, "rubber rich" domains within the epoxy composition are created. Those domains improve the toughness of the cured epoxy matrix once it is formed. However, while such modified epoxy compositions are tougher and less brittle at room temperature, improvements at lower temperatures prove to be, at best, marginal. Further, using the above-mentioned rubber-based material incurs processing problems due to an increase in viscosity of the adhesive mixture. For instance, polybutadiene-modified epoxies are difficult to process because of the limited solubility of polybutadiene in epoxy resins. As a result, the amount of polybutadiene that can be added is limited to the amount of polybutadiene which is soluble in the epoxy at room temperature. In many instances, the resulting compositions lack the amount of "rubber rich" domains necessary to toughen the composition especially at low temperatures. Polyacrylonitrile-butadiene copolymers compositions can be used as a substitute for polybutadienes. However, the epoxy compositions resulting therefrom are even less effective at lower temperatures.